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The majority of families in some of the US’s poorest cities do not have a broadband connection, according to a Financial Times analysis of official data that shows how the “digital divide” is exacerbating inequality in the world’s biggest economy.

US cities that have become synonymous with urban decay, such as Detroit and Flint in Michigan and Macon in Georgia, have household broadband subscription rates of less than 50 per cent, according to the US Census Bureau data. The median household income in all three is less than $25,000 a year.

Barack Obama has pledged to close the digital divide, and in 2010 the president unveiled a national broadband plan with the aim of giving “every American affordable access to robust broadband” by 2020.

But the new figures from the Census Bureau, which collected data on internet use at a sub-state level for the first time last year, show how hard it will be to hit that target in the next five years. There are still 31m households in the US without a home or mobile broadband subscription.

Susan Crawford, who served as Mr Obama’s special assistant for technology and innovation in 2009, warned: “we are creating two Americas where the wealthy have access . . . while others are left on a bike path, unable to join in the social and economic benefits that the internet brings”.

It had been thought that the rural make-up of much of the US was the main factor in a national broadband subscription rate that is just 73.4 per cent, behind other developed nations such as the UK and Germany, which have rates of 88 per cent. About 67 per cent of households in rural areas have broadband internet service, compared to 75 per cent of urban households.

But the new Census Bureau statistics show a huge disparity among US cities and towns, with a gap of 65 percentage points between those with the highest and lowest subscription rates.

The problem is most acute in urban areas where the typical cost for the most basic broadband packages is too expensive for some. The OECD ranks the US 30th out of 33 countries for affordability, with an average price of $44 a month, compared with $26 for the UK., $22 for Greece and $16 for South Korea, based on speeds of 2.5 Mbps.

The top of the US league table is dominated by prosperous growing towns such as Flower Mound in Dallas-Fort Worth and Timberwood Park outside San Antonio, which have broadband subscription rates of 95 per cent. The pair have median household incomes of $117,000 and $104,000 respectively. The rates in San Francisco and New York are 82 per cent and 74 per cent.

There is a very strong correlation with race and income. Just 45 per cent of households with an income of less than $20,000 a year have broadband whereas the rate for those earning $75,000 or more is 91 per cent. About a third of African American and Hispanic households are unconnected compared to 20 per cent for white households and 10 per cent for Asian households.